My guess is Oracle's tool is querying the operating system for CPU usage, and not querying Vertica's system tables. Between the OS and Vertica, CPU readings can be very different.

To look at the CPU usage from Vertica's perspective, use Management Console or query Vertica's system tables yourself.

Many DB's will hold onto the CPU's without yielding to the OS, whether or not the CPU's are actually doing any work. This is by design and is important for database performance. But it makes the CPU's look busy (from an OS perspective) even when they are quiet.

Also, look-up resource pools in the Vertica docs and read about cpuaffinityset and cpuaffinitymode.